No main equipotential bonds

[andyb]

But how does it 'become live' if it's not bonded?

The very fact that it's not bonded could result in a potential between an exposed conductive part and an extraneous conductive part, that extraneous conductive part could be a pipe in a bathroom for example.

If bonded correctly there would be no potential. So not live as you put it.

 

[Barry White]

wrong quote please delete

 

[Deleted member 9648]

Its purpose is to keep all conductive exposed parts at the "SAME" potential or as close to it as possible so as its bonded to earth if it has a potential because of a fault the earth in the zone should be at the same or close to the potential so reduce or eliminate the risk of a shock.
In layman terms without it a fault could make the pipes live resulting in an electric shock.

It may be at earth potential but is it equipotential to the rest of the earthed metalic electrical instalation. It needs to be kept equipotential in case a fault occurs on an immersion heater etc. Hence they need to be joined.

The reason I have gone into argumentative mode is that the sort of statements made above are one of the reasons there is so much confusion on main bonding. The inference is that bonding is there to prevent the pipes becoming live in the event of a live wire/part coming into contact with metallic pipes. This is NOT the reason for main bonding. This is one of the misguided beliefs which leads to people claiming plastic fittings on copper pipework have to be changed to metallic and other such nonsense.

Main bonding is there to negate the effect of a metallic service introducing the reference zero volts of earth into an electrical installation. Without main bonding the effect on a person in contact with an exposed conductive part such as the case of a kettle during a fault, with their hand on a tap would be the same as holding the kettle whilst stood barefoot on wet ground outside.
AT NO POINT IS THE TAP 'LIVE' IF IT'S NOT BONDED.

 

[Barry White]

you have just said what I said quote"Main bonding is there to negate the effect of a metallic service introducing the reference zero volts of earth"
So with your above quote in laymans terms we bond the services to the met so they are at the same potential (you referenced at 0v)

We can go on forever with kettle faults and touching a tap etc. I have seen live taps and showers and theres lots of posts on this forum about them. I work mainly in an engineering enviroment so bet others including yourself have seen more.
If the tap was not bonded and plastic pipe was used the tap would be isolated except for the water in the pipe which would reduce the severity of the shock.
I never said the pipe was live I said it could become live in fault conditions then anyone touching it and an earthed exposed metalic part would indeed get a shock
The plastic fittings is another argument.

 

[Deleted member 9648]

you have just said what I said quote"Main bonding is there to negate the effect of a metallic service introducing the reference zero volts of earth"
So with your above quote in laymans terms we bond the services to the met so they are at the same potential (you referenced at 0v)

We can go on forever with kettle faults and touching a tap etc. I have seen live taps and showers and theres lots of posts on this forum about them. I work mainly in an engineering enviroment so bet others including yourself have seen more.
If the tap was not bonded and plastic pipe was used the tap would be isolated except for the water in the pipe which would reduce the severity of the shock.
I never said the pipe was live I said it could become live in fault conditions then anyone touching it and an earthed exposed metalic part would indeed get a shock
The plastic fittings is another argument.

You miss the point entirely. It is the 'earthed exposed metallic part' as you put it which will experience a rise in potential in the event of a fault between energised conductors and exposed conductive parts,not the pipe.
Main bonding is not there to stop pipes becoming live in the event of faults.
And no,I have never seen a live pipe except on old installations with no earthing system except a suspect water main.
The last 'live pipe' I saw turned out to be a plumber causing a leak which soaked the floor,passing through a hole in the floor was a vermin damaged cable which effectively livened up the pool of water. The plumber kneeling in the water got a belt every time he touched the (unbonded) water main,he assumed the pipe was live when in fact it was the pool of water conducting to a pipe at 0v earth potential.

 

[Barry White]

part quote from wirepuller
"You miss the point entirely. It is the 'earthed exposed metallic part' as you put it which will experience a rise in potential in the event of a fault between energised conductors and exposed conductive parts,not the pipe."

So an immersion heater has an earth fault the tank and pipework are not conected to earth. It will have mains voltage both the tank and the pipework so anyone touching the pipe and an earthed exposed conductive part (metal kettle under no fault) would get a shock it would be the pipe that rose in potential against the 0v of the earthed exposed conductive part.

To try and prevent this we bond the pipework to the met to try and keep it at 0v

quote wirepuller
"The last 'live pipe' I saw turned out to be a plumber causing a leak which soaked the floor,passing through a hole in the floor was a vermin damaged cable which effectively livened up the pool of water. The plumber kneeling in the water got a belt every time he touched the (unbonded) water main,he assumed the pipe was live when in fact it was the pool of water conducting to a pipe at 0v earth potential."

agree with above statment

 

[Deleted member 9648]

part quote from wirepuller
"You miss the point entirely. It is the 'earthed exposed metallic part' as you put it which will experience a rise in potential in the event of a fault between energised conductors and exposed conductive parts,not the pipe."

So an immersion heater has an earth fault the tank and pipework are not conected to earth. It will have mains voltage both the tank and the pipework so anyone touching the pipe and an earthed exposed conductive part (metal kettle under no fault) would get a shock it would be the pipe that rose in potential against the 0v of the earthed exposed conductive part.

To try and prevent this we bond the pipework to the met to try and keep it at 0v

quote wirepuller
"The last 'live pipe' I saw turned out to be a plumber causing a leak which soaked the floor,passing through a hole in the floor was a vermin damaged cable which effectively livened up the pool of water. The plumber kneeling in the water got a belt every time he touched the (unbonded) water main,he assumed the pipe was live when in fact it was the pool of water conducting to a pipe at 0v earth potential."

agree with above statment

Still unbelievable!

For your reason for main bonding to work it would be a requirement for all metallic pipework in a property to be electrically continuous, which goes back to my point about plastic fittings. Have you ever stopped to consider why it is a requirement to main bond at the point of entry? How is that requirement compatible with a pipe connected to the hot tank which has plastic fittings between it and the point of bonding?
It is compatible because bonding has nothing to do with pipes becoming live!

 

[Barry White]

I am out an electrician who has never seen a pipe live and thinks a metalic pipe coming up from the ground is at the same potential as the met going around in circles here.
As for plastic fittings you introduced them to the post that was in laymans terms.
you win I must be wrong

 

[Deleted member 26818]

Here's how I see it:
An extraneous-conductive part may have a resistance to earth of 0.05ohms.
The Ze on a TN-C-S installation may be 0.35ohms, Ze on a TN-S installation 0.8ohms and on a TT installation anything.
This means there will be a difference in potential between the installation earthing and the exposed-conductive part.
Current will flow.
The current could be due to an earth fault in the installation.
However due to the manner our power is distributed there will also be neutral current.
This neutral current will not be just from the installation but will be from any other installation fed from the same origin (sub station).
Equipotential bonding equalises the difference in potential reducing the likelihood of current flowing from the installation earthing to the extraneous-conductive part.

 

[GEOFF S]

Its simples

Forget zero reference, okay. Fault occurs, voltage appears on exposed conductive part. With main bonding in place you transfer a voltage to the extraneous conductive part to limit touch voltage. Thats the purpose of Main Protective Bonding.

Cheers